1. Field of the Invention
The present invention generally relates to volumetric leak detection devices and methods and linear displacement detection devices and methods. More specifically, the present invention relates to a laser based linear displacement monitor that can be utilized to detect linear displacement of a surface and to detect linear displacement of a surface of a liquid in an enclosed volume to thereby detect any leak of the liquid from the volume.
2. Discussion of the Related Art
In 1985, the U.S. Environmental Protection Agency (EPA) estimated that there were approximately 3-5 million underground storage tanks containing hazardous substances or petroleum products in the United States alone. The EPA further estimated that approximately 100,000 tanks were leaking and that another 350,000 were expected to leak within the next five years.
It can be appreciated that substances and products leaking from such underground storage tanks present both an environmental and health hazard. The substances or products can leak into the ground and aquifers and the like, in the process contaminating same. Thus, it can be appreciated that such leaking underground storage tanks present a very serious problem.
On Sept. 13, 1988, the Environmental Protection Agency, charged with registering all underground storage tanks under the Resource Conservation Recovery Act, issued new rules to prevent leaks of petroleum and other toxic substances from underground storage tanks. Tank owners are required to furnish positive proof that a tank does not leak. The EPA estimated that only 5% of the affected tanks have leak detection systems.
One set of rules issued by the EPA applies to existing tanks, while another set applies to tanks installed after December, 1988. Tanks more than 25 years old must have leak detection systems installed within the next year, while newer tanks will have up to five years to meet such requirements.
The EPA is not alone in issuing rules designed to prevent and correct leaking of underground storage tanks containing toxic substances. Other countries throughout the world have also formulated legislation to ensure that tanks and contains, both above and below ground, be measured on a periodic basis to determine if they are leaking, thereby to determine the integrity of the tank.
The National Fire Protection Agency (NFPA), has established an optimum leak testing rate of 0.05 gallons per hour. See NFPA 329, Underground Leakage of Flammable and Combustible Liquids. However, such a sensitivity is difficult to attain, especially for tanks having a capacity of greater than 10,000 gallons.
The detection of leaking of tanks is called volumetric leak detection. A variety of systems have been employed to detect leaks in storage tanks.
Existing systems for detecting leaks include gauge systems such as float gauges, hydrostatic pressure columns and sonic or radar systems. However, such systems require difficult tank configurations during testing, such as a sealed tank, and a completely full tank. Additionally, these systems cannot attain an accuracy of plus or minus 0.05 gallons per hour.
Another method that has been used to detect volumetric leaks involves the use of a laser interferometer distance measurement system. In such system, a laser beam is reflected off of a corner cube reflector mounted on a float that floats on the surface of the substance in a tank. It has been indicated that in such a system leaks of about 0.1 gallons per hour were detectable.
A major problem with detecting volumetric leaks of substances such as petroleum products, is that for very small leaks, measurements must be made over a long period of time. However, during such period of time, a variety of influences can affect the measurement such as vaporization of a substance, vibration, temperature, and equipment response. Thus, it is very difficult to achieve more than a high degree of sensitivity, the ability to measure minute leas, utilizing prior art detectors.
To be sure, there are some volumetric leak detection systems that can attain a reasonable degree of accuracy in detecting small leaks. However, such systems generally are very elaborate and too expensive for small businesses and individuals.